1. Field of the Invention
This invention relates to a honeycomb core panel made of thin sheets of metal such as titanium. Such a panel comprises a honeycomb core placed between a pair of face sheets. Usually, the core is constituted by a plurality of corrugated ribbons or strips which are connected together by welding or the like to form a honeycomb construction. The face sheets are fixedly secured to the side edges of the core strips by welding or diffusion bonding. Such a construction is very lightweight and is extremely sturdy. The panel of this type is used usually in an airplane and ship.
2. Description of the Prior Art
To facilitate the welding of the face sheet to the honeycomb core, each of the core strips constituting the core has a flange formed on each of the opposite side edges thereof. These flanges are integral with the core strip, and are formed during the time when the corrugated core strip is formed from a metal strip serving as a flat plate by punching. The flange is formed by bending the side edge of the core strip so that the flange is corrugated in perpendicularly with respect to the core strip. The core strip has valley portions and plateau portions. The above bending operation causes wrinkles at the valley portions of the flange member. In the formation of the honeycomb core, the core strips are arranged in such a manner that the flanges of each core strip overlap the flanges of its adjacent core strip, respectively, thereby providing a honeycomb configuration. Generally, the flange assumes a "joggle" condition (that is, a slightly inwardly bent condition) at each valley portion of the strip, thereby facilitating the honeycomb formation. That portion of the flange disposed at the plateau portion of the core strip slides over that portion of the flange disposed at the valley portion of its adjacent core strip. By doing so, the flanges jointly provide sufficient flat surfaces to enable the face sheet to be fixedly secured thereto. Such a core strip and a method of producing the same are disclosed in Japanese Patent Examined Publication No. 62-47711.
In the above prior art, the flanges are bent in the same direction at the opposite side edges of all of the core strips. Therefore, while welding the uppermost core strip and its adjacent core strip together, wrinkles are present in a concentrated manner at those portions of the flanges disposed at the valley portions or the plateau portions, so that the thickness of the overlapped flanges is more than twice the thickness of the flange. Therefore, it is difficult to bond the face sheet uniformly to the core strips at a later stage. This particularly limits a demand for an increased thickness of the core strip. Thus, the conventional core strips could not be increased in thickness.